There are currently issues in Debian testing (8.1) due to an upgrade of MySQL to version 5.6 and an incompatibility with the version of package libmyodbc (5.1.10-3) available from the repository.This results in res_odbc.so causing Asterisk to crash with a Floating point exception.

The solution I have found is to download a new ODBC driver direct from mysql.com and install it as follows (assuming an x64 system):